Re: [Xen-devel] [PATCH 1/2] page-alloc/x86: don't restrict DMA heap to node 0

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.08.16 at 11:58, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 10/08/16 10:23, Jan Beulich wrote:
>> --- a/xen/arch/x86/numa.c
>> +++ b/xen/arch/x86/numa.c
>> @@ -355,11 +355,21 @@ void __init init_cpu_to_node(void)
>>      }
>>  }
>>  
>> -EXPORT_SYMBOL(cpu_to_node);
>> -EXPORT_SYMBOL(node_to_cpumask);
>> -EXPORT_SYMBOL(memnode_shift);
>> -EXPORT_SYMBOL(memnodemap);
>> -EXPORT_SYMBOL(node_data);
>> +unsigned int __init arch_get_dma_bitsize(void)
>> +{
>> +    unsigned int node;
>> +
>> +    for_each_online_node(node)
>> +        if ( node_spanned_pages(node) &&
>> +             !(node_start_pfn(node) >> (32 - PAGE_SHIFT)) )
>> +            break;
>> +    if ( node >= MAX_NUMNODES )
>> +        panic("No node with memory below 4Gb");
>> +
>> +    return min_t(unsigned int,
>> +                 flsl(node_start_pfn(node) + node_spanned_pages(node) / 4 - 
>> 1)
>> +                 + PAGE_SHIFT, 32);
> 
> You have moved the -1 and -2 inside the flsl() call, which alters its
> behaviour quite a bit.  Is this intentional or accidental?

This is intentional, and their original placement was only not too
wrong because of the effective use of zero in place of what is
now node_start_pfn(node). (Obviously the division by 4 alone
could have gone in either place, but the "- 1" should have been
inside the flsl() even before imo.)

Jan


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